docstr: Return coordinates of fiducial points in I_r; C 
docstr_tok: ["Return","coordinates","of","fiducial","points","in","I_r",";","C"]
code: def build_C_paddle(self):
      """Return coordinates of fiducial points in I_r; C"""
      F = self.F
      ctrl_pts_x = paddle.linspace(
          -1.0, 1.0, int(F / 2), dtype="float64"
      )
      ctrl_pts_y_top = -1 * paddle.ones([int(F / 2)], dtype="float64")
      ctrl_pts_y_bottom = paddle.ones([int(F / 2)], dtype="float64")
      ctrl_pts_top = paddle.stack([ctrl_pts_x, ctrl_pts_y_top], axis=1)
      ctrl_pts_bottom = paddle.stack(
          [ctrl_pts_x, ctrl_pts_y_bottom], axis=1
      )
      C = paddle.concat([ctrl_pts_top, ctrl_pts_bottom], axis=0)
      return C
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import math
  import paddle
  from paddle import nn, ParamAttr
  from paddle.nn import functional
  import numpy
label_desc: Use image node_id 3 for calling the GridGenerator obj's underlying member method code with example usage: obj.build_C_paddle() and returns: C